This invention relates to an optically readable record carrier of the inscribable type having a recording layer intended for recording an information pattern of optically detectable recording marks wherein a servo track is provided exhibiting a periodic track modulation which can be distinguished from the information pattern.
The invention additionally relates to apparatus for manufacturing a record carrier including an optical system for scanning a radiation-sensitive layer of the carrier along a path corresponding to the servo track to be formed and a deflection device for deflecting the radiation beam so that the position of incidence of the beam on the radiation-sensitive layer is deflected in a direction perpendicular to the scanning direction in conformity with a control signal applied to the deflection device.
The invention also relates to apparatus for recording information on a record carrier including an arrangement for recording a pattern of recording marks representing the information in the servo track. The arrangement includes: a scanner for scanning the servo track with a radiation beam so that the radiation beam reflected or transmitted by the record carrier is modulated by the track modulation: a detector for detecting the reflected or transmitted radiation beam: and a circuit for deriving a clock signal whose frequency is determined by the track modulation from the radiation received by the detector.
The invention further relates to apparatus for reading a record carrier in whose servo track an information signal is recorded as a pattern of recording marks. The apparatus includes: a scanning device for scanning the servo track with substantially constant velocity by means of a radiation beam: the radiation beam reflected or transmitted by the record carrier being modulated by the track modulation and the pattern of recording marks: a detector for detecting the reflected or transmitted radiation beam: a circuit for deriving an information signal representing the recorded information from the radiation detected by the detector, and a circuit for deriving a clock signal whose frequency is dictated by the track modulation from the radiation detected by the detector.
This type of record carrier including associated apparatus are known from German patent document Offenlegungsschrift No. 3100421.
This conventional record carrier has a spiral servo track exhibiting a track modulation of constant frequency. As the spiral servo track is scanned by a radiation beam during reading and/or recording, this track modulation modulates the radiation beam. This modulated beam is detected and from the modulation a clock signal is derived which is utilized for controlling the recording and/or reading process.
The servo track is divided into information-recording areas between which synchronization areas are interposed. The information-recording areas are intended for recording the information. The synchronization areas contain position information in the form of the address of the adjacent information-recording area. During scanning the position information in the synchronization areas, it may appear possible to derive from the reflected radiation beam the identity of the portion of the record carrier that is being scanned. This would enable a specific portion of the disc to be located rapidly and accurately.
However, the conventional record carrier has the disadvantage that the information-recording areas are constantly interrupted by synchronization areas. This is a drawback, in particular when EFM-encoded information is recorded on the record carrier. This is because such a recording method requires an uninterrupted information-recording area.